Financial Instruments - Narrative (Details) Bcf in Billions	12 Months Ended
	Sep. 30, 2025 USD ($) counterparty Bcf	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Foreign currency forward contracts duration maximum	5 years
After tax net hedging gains in accumulated other comprehensive income (loss)	$ 19,900,000
After tax net hedging gains reclassified within twelve months	35,700,000
Fair market value of derivative liability with a credit-risk related contingency	1,900,000
Hedging collateral deposits	0	$ 0	$ 0	$ 91,670,000
Foreign Currency Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Hedging notional amount of forecasted transportation costs	$ 44,100,000
Over the Counter Swaps, No Cost Collars and Foreign Currency Forward Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Number of counterparties in which the company holds over-the-counter swap positions | counterparty	18
Number of counterparties in net gain position | counterparty	13
Credit risk exposure per counterparty	$ 3,000,000
Maximum credit risk exposure per counterparty	8,700,000
Collateral received by company	$ 0
Cash Flow Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Hedge duration	5 years
Cash Flow Hedges | Natural Gas Bcf
Derivative Instruments, Gain (Loss) [Line Items]
Nonmonetary notional amount of price risk cash flow hedge derivatives, natural gas (in Bcf) | Bcf	414.3